Hygrosensitive element

ABSTRACT

A HYGROSENSITIVE ELEMENT WITH A COATING APPLIED TO A BASE AND CONSISTING OF A HYGROSCOPIC SALT AND A BINDING AGENT AND A METHOD OF ITS MANUFACTURE ACCORDING TO WHICH A FLEXIBLE ELECTRIC INSULATING FILM IS PULLED UNIFORMLY AND CONTINUOUSLY THROUGH A SOLUTION OF GELATIN FOR PRODUCING A UNIFORM LAYER OF GELATIN ON SAID FILM SAID LAYER BEING SUBSEQENTLY IMPREGNATED WITH AN AQUEOUS SOLUTION OF A HYGROSCOPIC SALT WITH TANNING COMPONENTS SO THAT THE SALT WOULD BE DISTRIBUTED UNIFORMLY OVER THE LAYER OF GELATIN, THE FILM COATING IT THEN DRIED, EXPOSED TO LIGHT FOR TANNING THE GELATIN AND TE STRIP IS CUT INTO SEPARATE FILM ELEMENTS.

Jtll- 1973 P. s. GABRUSENOK .712860 HYGROSENSITIVE ELEMENT Filed Nov. 19, 1968 I I llll'l United States Patent US. Cl. 204-195 W 3 Claims ABSTRACT OF THE DISCLOSURE A hygrosensitive element with a coating applied to a base and consisting of a hygroscopic salt and a binding agent and a method of its manufacture according to which a flexible electric insulating film is pulled uniformly and continuously through a solution of gelatin for producing a uniform layer of gelatin on said film, said layer being subsequently impregnated with an aqueous solution of a hygroscopic salt with tanning componentsso that the salt would be distributed uniformly over the layer of gelatin, the film coating is then dried, exposed to light for taming the gelatin and the strip is cut into separate film elements.

The present invention relates to a hygrosensitive ele ment for electrolytic humidity responsive devices used in combination with appropriate electrical circuitry in systems for remote measurement, recording and automatic control of humidity in air-conditioning systems and other installations, and to methods of manufacturing these elements.

Such humidity sensitive devices will be referred to as air-humidity detectors and it is to be understood that they are applicable to the measurement of the humidity of other gases too, provided they do not attack the materials of the detector.

The electrolytic air humidity detectors known in the art comprise a base or backing or support with electrodes rigidly fastened thereto and a hygrosensitive coating applied to the base on top of the electrodes, said coating containing a hygroscopic salt and a film-forming binding agent. In such a case the hygrosensitive element is an integral part of the detector. This, as will be explained below, is the main cause of insuflicient stability and interchangeability of the currently used electrolytic air-humidity detectors.

One of the main objects involved in increasing the stability and interchangeability of the electrolytic detectors amounts to making a hygrosensitive coating of uniform thickness and concentration and retaining this uniformity in the course of operation. This object cannot be achieved unless the process of application of the hygrosensitive coating is continuous for each batch of detectors because the beginning and end of each process are inevitably marked by some transitional steps exerting a different effect in each particular case on the thickness of the coating applied.

Besides,.the hygrosensitive coating must be applied to a homogeneously smooth surface which is free from cracks, sharp changes of shape, joints between different materials, otherwise the capillary forces and adhesion gradient on the base surface may lead to local thickening of the applied coating and to displacement of the hygrosensitive substance during detector operation owing to inconstancy in time of the capillary and adhesion forces.

Of the known methods of application of the hygrosensitive coating the most commonly used are methods in which each detector is dipped into a film-forming hygroscopic solution and uniformly withdrawn therefrom, or the solution is applied to the surface of the detector with a brush.

3,712,860 Patented Jan. 23, 1973 The above methods fail to ensure high-quality hygrosensitive coatings of the air-humidity detectors.

Intermittent application of the coating, irregular surface, and heterogeneous materials on the surface of detectors (electric insulating base and metal electrodes) preclude the production of a hygrosensitive coating of uniform thickness and fail to ensure the constancy of thickness in the course of detector operation which necessitates individual calibration and setting of each detector during manufacture and leads to insufiicient stability of calibration characteristics in time.

It is, therefore an object of the present invention to provide a hygrosensitive element featuring high stability and interchangeability.

Another object of the present invention is to provide a method of batch production of said hygrosensitive elements.

Still another object of the invention resides in providing an electrolytic detector capable of using the abovedescribed hygrosensitive elements.

With these and other objects in view, the present invention aims at providing a hygrosensitive element with a homogeneous smooth surface of the base and a hygrosensitive coating of uniform thickness, said element being a separate detachable part of the detector, and developing a method of manufacturing the hygroscopic elements, said method ensuring continuity of application of the hygroscopic coating to the element base.

This aim is achieved by providing a hygrosensitive element which, according to the invention, has its coating uniformly applied to a homogeneous, flexible dielectric film.

The flexibility of the backing makes it possible to apply uninterruptedly the hygrosensitive coating to a continuously moving strip, while the homogeneity of said strip ensures stability of the coating thickness along the strip length.

It is practicable to provide for rigid connection of and electric contact with the hygrosensitive element by the use of electrodes placed on the hygrosensitive element.

A method of manufacturing hygrosensitive elements according to the invention consists in pulling a flexible strip, e.g. a dielectric film, continuously and at a uniform speed through a solution of gelatin to form a gelatin layer of uniform thickness on said film which layer is then impregnated with an aqueous solution of hygroscopic salt and an added tanning component so that the salt is spread uniformly throughout the layer of gelatin; then the obtained coating is dried, exposed to light for tanning of gelatin and cut into separate film elements.

For applying the hygrosensitive coating it is preferred to pull the film through a 10% solution of gelatin at a temperature of 36 C. then through a hygroscopic aqueous solution of lithium chloride with a specific density of from 1.032 to 1.065 g./cm. at 20 C. with the addition of 5 to 20 ml. of aqueous solution of potassium bichromate saturated at 20 C. per litre of said solution.

Now the invention will be better understood from a description of an embodiment given by way of example of a hygrosensitive element and detector with reference to the accompanying drawings in which:

FIG. 1 shows a hygrosensitive element of the present invention;

FIG. 2 is a sectional view of an air-humidity detector with the element of FIG. 1.

A hygrosensitive element 1 has a film support (FIG. 1) comprising a triacetate flexible strip whose surface is covered with a hygrosensitive coating 15 to 20 microns thick.

Glued to the ends of the hygrosensitive element are two electrodes 2 made from anticorrosion metal foil.

The electrolytic air-humidity detector comprises an electric insulating base 3 (FIG. 2) to which a hygrosensitive element 6 is fastened by contact plates 4 and screws 5. On top, the detector is provided with a protective casing 7 with a fine-meshed metal screen 8.

The hygrosensitive eelments are manufactured, according to the invention, as follows.

A triacetate support of photographic film in the form of a long strip moving round a cylindrical shaft and contacting at one side a 10% aqueous solution of gelatin at 36 C. is pulled through said solution at a uniform speed of 300 cm./min. so that the surface of the backing becomes covered with a layer of gelatin 15 to 20 microns thick, accurate within Then, after the coating is dried, the film is then pulled through an aqueous solution of lithium chloride with a specific gravity of from 1.032 to 1.065 g./cm. at 20 C. with the addition of 5 to 20 ml. of aqueous solution of potassium bichromate saturated at 20 C. per litre of said solution. The strip is pulled at a speed of 1 cm./min., the solution temperature being to 18 C. so that the gelatin is impregnated with the solution to of its thickness. Then the gelatin coating is dried in the course of 5 minutes at 50 to 80 C. being simultaneously exposed for 30 minutes to the light of a conventional 100 w. incandescent lamp placed at a distance of 50 cm. from the film.

The dried film is cut into strips of equal length and width and the ends of these strips are provided with gluedon plates 0.05 to 0.1 mm. thick made of gold or silver foil.

By pulling the film in succession through the film-forming and hygroscopic solutions, it is possible to ensure a high uniformity of distribution of lithium chloride, over the area of gelatin coating while in the previous one stage coating, the film which is pulled only once through a mixture of the film-forming and hygroscopic solutions prevents the gelatin from being used as a film-forming agent; gelatin in this case loses its gelling ability which atfects adversely the uniformity of coating thickness.

Inasmuch as the above described hygrosensitive element and detector and the method of their manufacture may vary within the spirit and scope of the appended claims it will be understood that the description above does not restrict the invention to this particular embodiment.

What is claimed is:

1. An electrolytic humidity responsive device comprising two electrodes secured to a hygrosensitive element, said element comprising a base with a coating applied to said base, said coating consisting essentially of a gelatin, a gelatin tanning component and a hygroscopic salt, said coating being substantially uniform in thickness and said base being a flexible, substantially smooth dielectric film.

2. A device as claimed in claim 1, wherein said hygroscopic salt is lithium chloride and said gelatin tanning component is potassium bichromate.

3. A device as claimed in claim 1 wherein said sensitive element is secured at said electrodes so as to be freely suspended therebetween.

References Cited UNITED STATES PATENTS 2,458,348 1/1'949' Cleveland 73-3365 2,609,688 9/1952 Larach 73-3365 2,816,067 12/1957 Keidel 204-129 2,962,897 12/1960 Muller 73-3365 3,045,198 7/1962 Dolan et a1. 324-71 3,058,079 10/1962 Jones 338-35 3,062,732 11/1962 'Keidel 204-129 3,188,283 6/1965 Cole 204- 3,350,941 11/1967 Misevich et a1 73-3365 1,842,544 1/1932 Freuder 106-125 1,851,166 3/1932 Kienninger 106-125 2,505,734 4/1950 Freud 106-125 FOREIGN PATENTS 181,349 3/ 1965 U.S'.S.R. 204-195 TA-HSUNG TUNG, Primary Examiner US. Cl. X.R. 

